Posterior Neck - LO2

2. What is the Root of Neck (RON)? Which structures (e.g. neurovasculature, muscles, & bones) are associated with the RON, and what are the classic anatomical relationships of these structures to one another?

The root of the neck (RON) is the nexus between the neck, thorax, and upper limbs. The RON is the proximal attachment site for many neck muscles and transmits important neurovasculature (e.g. common carotid aa., jugular vv., subclavian aa. & vv., vagus nn., and trunks of the brachial plexus).

The anterior scalene m. is an important anatomical landmark for understanding the neurovasculature of the root of the neck. There are four classic anatomical relationships to understand:

• 1. the anterior scalene m. is sandwiched between the subclavian v. (anterior) and subclavian a. (posterior),

  2. the anterior scalene m. establishes the borders for the divisions of the subclavian a.,

  3. the anterior scalene m. is immediately posterior to (and closely associated with) the phrenic n. as the phrenic n. descends the neck and the root of the neck, and

  4. the anterior scalene m. is separated from the middle scalene m. by the roots (ventral primary rami of spinal nn.) and trunks of the brachial plexus and subclavian a..

The phrenic n. (C3,4,5) descends from the cervical plexus through the root of the neck (just anterior to, and upon the anterior scalene m.) before entering the thorax between the subclavian a. & v. The phrenic n. is efferent (motor) and afferent (sensory) to the diaphragm and afferent (sensory) to the pericardium and diaphragmatic pleura.

The vagus n. (CN X) is the major parasympathetic supply and conduit to the thorax and abdomen, and is the major innervation to muscles of the larynx and pharynx, and aspects of the head.

The R. and L. vagus nn. take different routes through the thorax. Both nerves descend the neck within the carotid sheaths, and cross anteriorly over the subclavian aa., deep to the first ribs. The R. vagus n. then sends a major branch (the R. recurrent laryngeal n.) inferiorly and then posteriorly around the R. subclavian a., lateral to the trachea, on a course for the larynx. The L. vagus n. sends the L. recurrent laryngeal n. inferiorly and then posteriorly around the concavity of the arch of the aorta, lateral to the trachea, also on a course for the larynx.